The only negative to the block offs is that you are polluting like a mo' fo' with the unused fuel and wouldn't pass an emissions inspection. Additionally, it might be possible that the unused fuel may burn up afx cans quicker, but I can't exactly comment on that as of yet, so it's just speculation.
I think that whether you have the block offs on or off doesn't reduce the amount of unburned fuel in the exhaust system. You are only changing the unburned fuel/air mix. You have no CAT so none of it is going to burn anyway.
Also if you dyno the bike, the map will be more efficient for a complete burn.
Without the CAT it will pollute more tho.....it's not as much as a 1956 chevy with a 427 and no emissions tho or an old VW bug from the 1960's...